1. Field of the Invention
This invention relates generally to digital communication systems and methods, and more particularly to a technique of estimating frequency and phase offset using the Least Square Method (LSM) in a synchronized code division multiple access (e.g SCDMA) burst receiver that was implemented, for example, in DOCSIS 2.0 standard.
2. Description of the Prior Art
Frequency and phase offsets are important parameters to estimate in a burst receiver. Those parameters are estimated during channel maintenance and verified during processing of each burst preamble. In at least one modem burst receiver, the frequency and phase offsets are estimated using a correlator output. In SCDMA applications, this technique may not be accurate enough for the following reasons:    1. Due to the structure of the framer, it is possible to find a difference of 128*16=2k chips between the center of the preamble (where the correlator estimates the phase) and the beginning of the data. In the case of, for example, 50 Hz frequency offset @ 1.28 Mbaud, this results in a phase shift of 2k*50/1.28e6*360˜30 degrees, which is obviously unacceptable. A technique for achieving an accurate estimation of the phase of the first spreading interval should therefore be employed.    2. In the worst-case scenario, only one mini-slot will be granted to a certain burst, resulting in only two active codes. As a result, only two training symbols may be processed before the phase would change in response to a frequency offset. In the case of a 50 Hz frequency shift @ 1.28Mbaud, for example, the phase change would be 128*50/1.28e6*360˜1.8 degrees. A method for achieving an accurate estimation of the frequency offset should therefore be utilized.
In view of the foregoing, a need exists in burst receiver applications, such as the SDCMA burst receiver implemented, for example, in DOCSIS2.0 standard, for a scheme to provide accurate estimations of the phase of the first spreading interval as well as accurate estimations of any frequency offset. The scheme would desirably provide a good tool to combat impulse and burst noise affecting the preamble.